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Biomedical subjects

R I Walker

Publications and source records attributed to R I Walker.

At least 73 records · Page 4Linked to original sources
PubMed1983

Pathogenicity of encapsulated Bacteroides melaninogenicus group, B. oralis and B. ruminicola subsp. brevis in abscesses in mice.

The pathogenicity of 27 clinical isolates of the Bacteroides melaninogenicus (BM) group and four clinical isolates of B. oralis and B. ruminicola subsp. brevis were investigated by inoculating them into mice and subsequently determining their ability to cause subcutaneous (SC) or intraperitoneal abscesses. Only 11 isolates of BM group and one B. ruminicola induced abscesses in mice, and all were found to be heavily encapsulated on recovery from the abscesses (more than 50 per cent of the organisms were encapsulated). When the other 23 isolates, however, were injected SC in combination with either Klebsiella pneumoniae, Haemophilus influenzae, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus or Streptococcus pyogenes, abscesses were formed in 16 of the 23 combinations. The Bacteroides spp. recovered from the mixed infection were heavily encapsulated. Capsules also formed in Bacteroides if the organisms were injected together with capsular material or formalin killed cells of K. pneumoniae or encapsulated Bacteroides sp. Once non-encapsulated or only slightly encapsulated strains acquired a capsule, they could induce abscesses on reinoculation into mice.

Abscess↗
PubMed1983

Antibiotic and clavulanic acid treatment of subcutaneous abscesses caused by Bacteroides fragilis alone or in combination with aerobic bacteria.

A subcutaneous abscess model was utilized in investigating the usefulness of various antimicrobial combinations in the treatment of mixed aerobic-anaerobic infections in mice. The infected animals were treated for seven days with single or combined antimicrobial therapy. The single agents used were penicillin, clavulanic acid, oxacillin, metronidazole, and gentamicin. The antimicrobial combinations used were penicillin plus clavulanic acid and metronidazole plus penicillin, oxacillin, or gentamicin. Administration of a single agent was effective in treating abscesses caused by a single susceptible organism. The only effective therapies for mixed infections were the combinations of penicillin plus clavulanic acid or metronidazole plus gentamicin. This study demonstrated the efficacy of penicillin and clavulanic acid in the treatment of infections caused by Bacteroides fragilis alone or in combination with beta-lactamase-producing aerobic bacteria.

Abscess↗
PubMed1983

In-vivo protection of group A beta-haemolytic streptococci from penicillin by beta-lactamase-producing Bacteroides species.

The incidence of persistent group A beta-haemolytic streptococci in tonsils, despite penicillin therapy, has increased in recent years. beta-Lactamase-producing organisms have previously been recovered from 74% of patients with persisting group A streptococci. We investigated the possibility that beta-lactamase-producing strains of Bacteroides spp. can protect streptococci from penicillin. A mixed infection was induced in mice in the form of a subcutaneous abscess involving a penicillin-susceptible group A streptococcus, and a beta-lactamase-producing strain of either Bact. melaninogenicus or Bact. fragilis. The infected animals were treated for seven days with parenteral penicillin, penicillin and clavulanic acid or clindamycin. Penicillin treatment prevented the formation of abscesses in animals inoculated with group A streptococci alone, but not in those inoculated with group A streptococci and Bacteroides spp. We attributed this resistance to penicillin therapy, and the subsequent formation of abscesses in mice, to protection of the streptococci from penicillin by beta-lactamase-producing strains of Bacteroides spp. Effective therapy for mixed infections was achieved when clavulanic acid, a beta-lactamase inhibitor, was administered with penicillin. A similar effect was noted with clindamycin, which is active against both group A streptococci and Bacteroides spp.

Abscess↗
PubMed1983

Biphasic culture system for rapid Campylobacter cultivation.

We developed a biphasic culture system consisting of 4 ml of brucella agar (BA) and 6 ml of brucella broth (BB) in 25-cm2 tissue culture flasks, which were incubated in air (BB/BAa) or in a gas mixture of 5% O2, 10% CO2, and 85% N2 (BB/BAg). These media were also used with a supplement consisting of ferrous sulfate, sodium metabisulfite, and sodium pyruvate and incubated as above (FB/FAa and FB/FAg, respectively). Highly satisfactory growth of Campylobacter jejuni 301 was obtained with all medium-gas phase combinations provided that the number of viable cells in the inoculum was large (greater than or equal to 10(6)/ml). The use of FB/FAa permitted the inoculum to be reduced to 100 cells per ml. With an adjusted gas phase (BB/BAg and FB/FAg), near-optimal growth was obtained from an inoculum of 1 to 10 cells per ml. Under most of these conditions the generation time was approximately 90 min. During the logarithmic growth phase, the cells retained their typical spiral morphology and high motility. These media also proved to be highly satisfactory for the cultivation of fresh isolates as well as other stock strains of Campylobacter. When the broth phase of the cultures, after addition of 15% glycerol, was quickly frozen and maintained at -70 degrees C, all strains thus far examined were readily recoverable and satisfactorily cultivated without additional passage.

Agar↗
PubMed1983

Simple adult rabbit model for Campylobacter jejuni enteritis.

We tested the usefulness of the Removable Intestinal Tie Adult Rabbit Diarrhea model to establish Campylobacter jejuni infection in rabbits. The procedure involved ligation of the cecum, placement of a slip knot at the terminal ileum, and injection of the test inoculum into the mid-small bowel. The ends of the slip knot were externalized, and the tie was released 4 h later. Fifty-five rabbits received C. jejuni, and 16 received uninoculated medium as controls. Daily rectal swabs were positive for 2 weeks in infected rabbits. The diarrheal attack rate was 64% in infected rabbits and 0% in controls. Diarrhea was characterized by loose, mucus-containing stools after an incubation period ranging from 24 h to 6 days. When blood was obtained daily for culture from 30 rabbits for 4 days post-challenge, bacteremia was present in 96.3% 24 h after challenge but diminished to 5 of 19 (26.3%) at 96 h. Death occurred in 53% of rabbits and was always preceded by diarrhea. No control animal died. Only 5 of 35 animals experiencing diarrhea recovered. An indirect whole-cell enzyme-linked immunosorbent assay was used to determine serum immunoglobulin G responses. Mean titers rose from 1:198 preoperatively to 1:9,087 on day 28. Necropsy on eight infected and two control animals showed inflammatory lesions with ulceration in 62.5% and goblet cell hyperplasia in 75% of infected rabbits. We conclude that the Removable Intestinal Tie Adult Rabbit Diarrhea procedure is a simple, effective method to establish C. jejuni infection which mimics human disease.

Animals↗
PubMed1983

Infectivity of organisms recovered from polymicrobial abscesses.

The ability to cause subcutaneous abscesses in mice was used to identify the pathogens among the bacteria recovered from 13 clinical abscesses. A total of 35 isolates (30 anaerobes and 5 aerobes), 16 of which were encapsulated, were recovered from these abscesses. Encapsulated organisms included eight Bacteroides spp. (three Bacteroides asaccharolyticus and one strain each of Bacteroides oralis, Bacteroides intermedius, Bacteroides biacutus, Bacteroides vulgatus, and Bacteroides ruminicola subsp. brevis), three anaerobic gram-positive cocci, two Clostridium spp., and two strains of Escherichia coli. Single organisms, or combinations thereof, obtained from these abscesses were inoculated subcutaneously into mice. All but one of the encapsulated organisms were able to cause abscesses by themselves and were recovered from the abscesses when inoculated with other organisms. Seven non-encapsulated organisms which were also recovered mixed with the encapsulated organisms were never able to cause abscesses nor could they be recovered after they were injected alone. Thirteen strains that did not induce abscesses when injected by themselves into mice survived when injected with other organisms which were encapsulated. In three instances, pairs of non-encapsulated organisms belonging to the last group were able to induce an abscess and survive in it when inoculated together. It was shown that the possession of a capsule by a clinical isolate increases the likelihood that it is a major contributor to the infectious process.

Abscess↗
PubMed1983

Rat intraperitoneal sepsis--a clinically relevant model.

The pathologic changes in septic shock, a disease state involving several hemodynamic and metabolic parameters, are not completely understood. Because research on animals can provide information vital to treating disease in humans, and because of the increasing constraints on clinical trials with humans, a clinically relevant animal sepsis model has been developed using adult male Sprague-Dawley rats. Sepsis was induced in large numbers of rats by IP injections of discrete quantities of live E coli organisms. The following elements were measured at specific times: MAP, CO, CVP, WBC, platelets, hemoglobin, hematocrit, PT, PTT, fibrinogen, clotting factors, glucose, blood gases, Ca++, Mg++, and TSP. The study shows that the model is easily replicated and relatively inexpensive, and that it can be used for detailed study in rats of several of the pathophysiological states characteristic of sepsis in humans.

Animals↗
PubMed1982

Association of prostacyclin production with resistance of C3H/HeJ mice to endotoxin shock.

Persistence of inflammatory cells in the microcirculation due to altered proportions of arachidonate metabolites could contribute to death from endotoxin (ET) shock. We tested this hypothesis by observing ET-induced cellular accumulations in capillaries of genetically resistant C3H/HeJ and sensitive C3HeB/FeJ mice after challenge with 1,000 micrograms of Salmonella typhi ET, a dose lethal only for the sensitive strain. These data were correlated with prostaglandin production by lung tissue. Six hours after challenge with ET, lung capillaries of sensitive animals were occluded with amorphous material and occasional polymorphonuclear leukocytes (PMNL). This inflammation, along with reduction in alveolar volume, was not observed in resistant mice. At this time only 10 PMNL/high-power field were seen with light microscopy in capillaries of resistant mice compared to 60 PMNL/high-power field in sensitive animals. Lung parenchymal tissue was excised from resistant and sensitive (C3H/HeN) mice six hours postchallenge with 800 micrograms of endotoxin and release in vitro of thromboxane A2 (TXA2) or prostacyclin (PGI2) over a 30-minute period was determined by radioimmunoassay. TXA2 and PGI2 released by lung fragments taken six hours after challenge with ET did not differ from normal levels of these substances in C3H/HeN mice. TXA2 release was normal at six hours in C3H/HeJ mice, but PGI2 was significantly increased (from 2.95 ng/mg to 5.73 ng/mg, P less than 0.005). The ratio of PGI2/TXA2 in resistant mice was 24.3 as compared to 10.3 in sensitive mice. Since PGI2 can reduce leukocyte adhesion, an increase in the ratio of this substance to TXA2 may be associated with resolution of PMNL from the pulmonary microcirculation of ET-resistant mice.

Animals↗
PubMed1982

Hematopoietic responses to lipopolysaccharide in C57BL/10Sn and C57BL/10ScN strain mice.

Inbred mouse strains C57BL/10Sn (Sn) and C57BL/10ScN (ScN) differ in response of their hematopoietic system to injection of lipopolysaccharide-W (LPS-W) in a manner similar to that observed for the LPS unresponsive C3H/HeJ and the paired responsive C3H/HeN strain mice. Responses of endogenous (E-CFU) stem cells as well as bone marrow and spleen-derived exogenous (CFU-s) stem cells, granulocyte-macrophage (GM-CFC) and macrophage (M-CFC) colony-forming cells were determined for Sn and ScN strain mice following an intraperitoneal injection of 10 micrograms LPS-W. Sn strain mice responded characteristically in terms of every parameter measured. Marrow-derived parameters reflected release of nucleated cells and early decrease of CFU-s, GM-CFC, and M-CFC followed by return toward control values. Peak splenic responses were observed within 4-5 days, whereas E-CFU increased significantly within 24 h after LPS-W. These responses were in marked contrast to those observed for the ScN strain mice, which were relatively unresponsive in terms of each parameter measured after LPS-W injection. These results show that the phenotypic expression of the defective LPS locus recently described in the ScN strain mice extends to those cells that control the response of the hematopoietic system to LPS, and is similar in every respect to those responses observed for the mutant LPS defective, C3H/HeJ strain mice.

Animals↗
PubMed1981

Association of Aeromonas sobria with human infection.

Fifteen Aeromonas isolates from various human infections and nine isolates from polluted water were identified as either Aeromonas hydrophila or Aeromonas sobria and examined for cytotoxigenicity, enterotoxigenicity, adherence to epithelial cells, and other virulence-associated factors, including proteases, lipases, elastases, and hemolysins. Two groups of organisms (I and II) were distinguishable based on differences in median lethal doses in mice and cytotoxicity for Y-1 adrenal cells. Group I clinical and environmental strains had median lethal doses of less than 10(7) colony-forming units, were cytotoxic, frequently possessed several virulence-associated factors, and had lysine decarboxylase-positive or Voges-Proskauer-positive phenotypes or both. Piliation of Aeromonas was associated strongly with ability to adhere to human buccal cells, and these characteristics were associated with group I strains. Group II clinical and environmental strains had median lethal doses of greater than or equal to 10(7) colony-forming units, were not cytotoxic, and usually were lysine decarboxylase negative or Voges-Proskauer negative or both. Clinical strains in group II exhibited enterotoxigenicity, which was not detected in group II environmental strains. A sobria was more frequently associated with human infections; 13 of the 15 clinical strains were A. sobria, and 2 were A. hydrophila. On the other hand, the majority of the environmental strains (seven of nine) were A. hydrophila.

Aeromonas↗